This invention relates to a refractory product for use in continuous casting. More particularly the invention is concerned with tubular refractory products for use in pouring of melt from the tundish to the mould. Flow of melt from the tundish into a mould is commonly controlled by raising or lowering of a refractory stopper rod from or to a seating position in the base of the tundish where there is located either a fixed sub-entry nozzle (SEN) or a tundish nozzle, built into the tundish base, onto which a sub entry shroud (SES) is fastened. In place of stopper rod valve closures, a slide gate control mechanism to which the SEN or SES is attached is also known.
Recently some steelmakers have been fitting to the underside of the tundish a fairly simple mechanism which enables quick changeover of such pouring tubes to minimise loss of time and production in replacing worn or damaged tubes. Such a tube-changer is described in GB-A-1 597 215 whilst another is disclosed in EP-A-0 192 019. When an SES is cracked or worn out the mechanism rapidly pushes out the used piece and drives a new tube into alignment underneath the metal stream, for example by means of a piston arrangement.
The present systems use an upper nozzle having a seating position to receive a flow control stopper located within a well block fixed into the tundish lining against which a stationary plate is fitted and incorporating a suitable jointing arrangement between the two components. A lower assembly is held in place against the underside of this stationary plate by the tube changer mechanism and comprises a moving plate and submerged pouring shroud jointed by a suitable arrangement and retained within a strengthening steel shell which serves to hold the two components firmly together and to withstand the pressures transmitted by the operating piston.
Whilst improvements have been made in the tube changing mechanisms since their introduction, there remain problems in ensuring adequate fitting of the respective mating surfaces of the tube, nozzle and upper or stationary plate and the lower or sliding plate of the tube changer and the submerged pouring shroud. If improper fitting of these refractory components occurs then air/oxygen leakage through the misfitting joints is possible with detrimental effect upon the quality of the steel. Air/oxygen penetrating the joints reacts with the alumina in the steel leading to build up of alumina deposits and clogging of the pouring tube. Such reaction also yields a problem manifesting itself as inclusions in the casting commonly identified as black spot.
Thus those in this field have hitherto sought to mitigate such problems by seeking to improve the tube handling and change-over systems leading to ever more complex and expensive handling systems.